Pain: Why is hardware painful?

Pain from Fixation Hardware

Tenderness
Hardware is well named. The screws and plates are hard and can be felt as tender points
under the skin. This type of pain is easy to understand and diagnose.Diffuse Pain
Even if not tender hardware can cause a diffuse aching pain. The reasons are not well
understood but may be due to the small electrical currents which are set up when a metal
object is placed in a salt solution. Some people's pain fibers are sensitive enough to be
stimulated by this current and feel pain as a result.